There are many sources of artificial lighting, from the very old arc and incandescent lamps, the middle-aged fluorescent lamps, to the new-aged laser and solid state lamps. While each of the these lamps may be suitable for many uses and application, none is very good for many uses. Carbon arcs are becoming almost non-existent, incandescent use is dropping, fluorescent is gaining, and solid state growing very fast. Even with all of this change we have not achieved a revolution in lighting. Incandescent lamps are good at one brightness, but they cannot be dimmed without radically changing color temperature. Most fluorescent lights have poor color rendering and with most white LEDs color rendering is no better. What is needed is a lamp whose color and/or color temperature is tunable in power spectral density and brightness.
Lamps using this advance in the state of art would have many uses from the scientific, medical, personal, and studio lights for film or video production, or for entertainment. These lamps, if put into arrays, could be used for lighting panels.
Large arrays of these lamps might be used for video displays in theaters or for outdoor displays. They can be used anywhere a repeatable controlled variable color or color temperature light is needed.
The most basic lamp is composed of a cell containing one phosphor in a supporting matrix that is illuminated by an exciting energy, in this case, ultraviolet (UV) light. The outer edges of the device are surrounded by a UV light source and this light source is covered by a housing which keeps the UV light in, and external light out. When the UV source is on it causes the phosphors in the matrix to fluoresce. Units so comprised would give a fixes spectral output, of that one phosphor. Furthermore its intensity (brightness) would also be fixed if the UV illumination level was fixed, thus it is not tunable. A lamp unit designed like this would be very similar to the volumetric light source described in U.S. Pat. No. 5,306,445 which is herein incorporated by reference. Reed, et al., U.S. Pat. No. 5,306,445 “Inorganic volumetric light source excited by ultraviolet light” is the keystone patent to this disclosure. Without the methods taught within it, the new embodiments disclosed here would not be possible. reed, et al. used—and I will also use—silica aerogel as support matrix for the Q-particle phosphors. If it were not for recent advances in research, and in the art of the manufacturing of Q-particle phosphors, now commonly called quantum dots, this advance would not be possible.
The preferred phosphors are t hose whose spectral curve is almost gaussian and have a half width at half maximum (hwhm) bandwidths of around 20-30 nm, cover the full visible spectrum, and are composed of cadmium sulfide or cadmium selenide. With careful selection and blending one can make up almost any visible power spectrum one wants. These nanocrystalline materials go by many names: nanoparticles, Q-particles, quantum dots, quantum nanodots, or nanocrystallites. There are two researchers who have companies that sell quantum dots that have utility: Nanoco, 48 Grafton Street, Manchester M13 9XX, UK and Paul O'Brien was issued the U.S. Pat. No. 6,379,635, which is herein incorporated by reference, for a “Process for preparing a nanocrystalline material.” The other is Nanomaterials and Nanofabrication Laboratories (NN-Labs) PO Box 2168/and Peng, et al. was issued a U.S. Pat. No. 6,869,545, which is herein incorporated by reference.
The first electrical fluorescent lamp patent was granted to Edison in 1907, U.S. Pat. No. 865,367, and is used x-rays to energize a phosphor. Since then many fluorescent lamps have been disclosed which advanced the art, but the color rendering from these lights was poor, and the search was on for a lamp with a high-color rendering index(CRI). That changed with the development of three-bank fluorescent lamps using UV light from the excitation of mercury vapor. The phosphors employed in these lamps have three different spectral distributions and the perceived color each distribution colors would be red, green, and blue. Among the first U.S. patents issued that advanced the art in this direction are: U.S. Pat. No. 3,748,517 issued to Haft in 1973 and U.S. Pat. No. 3,858,082 issued to Thornton in 1974. The art of fluorescent lamps was advanced again in U.S. Pat. No. 4,075,532. It was issued to Piper in 1987 and it demonstrates a two-band fluorescent lamp using phosphors that have a narrow “blue” emission spectrum, and a broad “yellow” emission spectrum to give white light. The art of a two-band fluorescent lamp was developed giving a less expensive bulb but poorer color rendering than the three-band bulbs, but better than a conventional one. U.S. Pat. No. 3,602,758 was issued to Thornton in 1971 and it illustrates a method for making a two-phosphor layer fluorescent lamp. This is achieved by coating a substrate with one layer of phosphors of one type, and putting another layer of different phosphors on top of that. UV light from a mercury discharge illuminates the first layer causing that layer to fluoresce and subsequently through the second causing that layer to fluoresce also and exit the lamp. By using this method, it enables the spectral power emissions of the two phosphors to be summed, giving a spectral power curve that neither alone could give. This method increased the efficiency of the phosphors, but color rendering was not very good. Hybrids of this process and the three-band method made a higher CRI bulb that is cheaper than a pure three-band bulb.
All of the fluorescent mercury discharge lamps mentioned above use one or more of the following types of phosphors: halophosphate phosphors, phosphate phosphors, silicate phosphors, aluminate phosphors, or tungstate phosphors. These phosphors have properties that allow them to work well in the environment of a mercury discharge arc. Most of these phosphors have multiple peaks or wider spectral bandwidth than phosphors used in cathode ray tubes.
U.S. Pat. No. 5,592,052 was issued to Maya in 1997 for a “Variable color temperature fluorescent lamp” and it teaches a method of making a fluorescent lamp having at least two phosphor coatings on the surface of the sealed lamp bulb. there is variable driving means which preferentially activates one phosphor and not the other phosphors. This allows the user to change the color temperature of the lamp by controlling parameters of the electrical driving signal, thus changing the light output to be more or less blue or red, or to balance the longer wavelengths perceived against the shorter wavelengths perceived. A real advance in the art was made by this patent: it is able to shift its color temperature by an electronic control unit. However, the color rendering in not as high as the more advanced three-band fluorescent lamps.
Florescent lamps have developed greatly over the years but there is no lamp that has a very high CRI and that is variable in color, temperature and brightness. Cathode ray tubes (CRTs) use different types of phosphors than conventional fluorescent lights. A CRTs CRT's phosphor functions by a electron beam, in vacuum, hitting a phosphor layer on a coated transparent substrate. Black and white CRTs that are used for television are composed of a mixture of blue and yellow phosphors to give a “white” light. The typical compositions for the blue emitter is a silver-activated zinc sulfide and the yellow emitter is silver-activated zinc-cadmium sulfide. Color CRTs use red green and blue phosphors and the composition of the typical phosphors are: for red in old pre-1966 tubes was gold-activated zinc-cadmium sulfide and common currently is an europium-activated yttrium oxysulfide; for green it is a copper-aluminum-activated zinc sulfide; for blue it is a gold-activated zinc sulfide. These phosphors have to work in the environment of a vacuum and in the presence of an electron beam. These phosphors have a relatively narrow spectral band width and are typically metal sulfides.
The difference between the phosphors for displays and lights is quite great. With displays you want a narrow bandwidth so you can more accurately portray saturated colors. With displays you are not trying to make a white light with a high CRI because you are not interested in the reflected light, but transmitted light. With lights, for illumination, the goal is to make a lamp that will render the environment accurately and not have problems with metamerism, and you are dealing with reflected light.
The colors of two objects are generally designated as being metameric if these objects have a different reflection spectrum, but nevertheless give the same color impression under a given kind of light, for example in daylight. Then if under another kind of light, for example an incandescent lamp, the color impression of these objects is different. This improved embodiment of a fluorescent lamp that I have developed overcomes many of these problems of color rendering and metamerism by having the ability to change the spectral power curve (color temperature) and/or brightness. A lot of lamps are good at color rendering but only at one brightness; others can be dimmed but have color rendering problems at different brightnesses.
There are many process that have been used in prior art in varying the power output of lamps: (1) by physical some methods using some sort of shutter that chops the light or partially obscures the lamps source: U.S. Pat. No. 4,281,897; by optical methods optically variable or transmissive or reflective filters: U.S. Pat. No. 4,127,322, U.S. Pat. No. 5,287,096; (2) by electronic methods that are analogous the physical and optical methods; (3) by Pulse Width Modulation (PWM) which is analogous to a variable physical light chopping shutter. The power source is either on or off and the ratio on to off determines the power output. To use PWM with light-emitting diodes (LEDs) one must use current limiting in order to operate the devices with a margin of safety: U.S. Pat. No. 4,001,663; (4) by controlling the parameters of the voltage and/or current flowing through the device. Some precautions must be taken when using LEDs because they can be destroyed by passing too much current through them; and (5) by having a plurality of lamps wired in parallel that can be switched on or off independently. Thus the optical power output is the sum of the lights that are turned on.
What I will use to power and control the lamps are devices like Silicon Laboratories programmable digital power controllers which provide closed-loop feedback control, system protection, and power management functions for switch mode power systems. The Si825x architecture combines a dedicated DSP-based control loop processor with an in-system programmable system management processor. With these smart power supplies the power output of each light can be programmed.
The teaching about a variable color RGB LED display is in U.S. Pat. No. 4,845,481 issued to Have in 1989 “Continuosly variable color display device.” He made the device to control the color on a readout display and this was accomplished by a PCM of power to and RGB LED display. Another teachings about a variable color RGB LED light unit is in U.S. Pat. No. 6,016,038 issued to Mueller, et al. in 2000 “Multicolored LED lighting method and apparatus”, the PWM method of controlling the power to the LEDs which may be computer controlled. The problem with these LED lamps is that they are not very good at illumination. The bandwidth of the R, G. B, source LED is too narrow to give a good color rendering, but it works very well if you want saturated colored light. The possible amount of colors is limited to the areas within the CIE triangle. The advantages of lamps that use LED is that they have a long life and are quite efficient, and therefore do not produce a lot of heat.
Other methods of lighting have been developed to give very high illumination with variable color and brightness. These systems have the same color space problems because they are using the three primaries: red, green, and blue.
A remote-controlled high-brightness projection using RGB tricolor mixing, but it uses conventional optics. The teaching about it is in U.S. Pat. No. 4,602,321 issued to Bornhorst in 1986 “Light source having automatically variable hue, saturation and beam divergence.”
Computerized high brightness projection and/or lighting systems using RGB tricolor mixing have developed recently: Constructed with conventional optics: U.S. Pat. No. 5,143,444 issued to Shields in 1992 “Computer controlled light with continuously variable color temperature, color, magnification, focus, and position.” Constructed with digital micromirror device (DMD), U.S. Pat. No. 6,454,440 issued to Yamamoto in 2002 “Illumination apparatus and projection type display apparatus using the same.” Constructed with LCD light gates: U.S. Pat. No. 6,623,144 issued to Bornhorst in 2003 “High intensity lighting projectors.”